This project has two major objectives. First, the development of the kitten corticotrigeminal projection will be studied using reduced silver stains, autoradiography, and electron microscopic methods. The time of arrival of corticotrigeminal afferents within the spinal trigeminal nucleus (pars interpolaris) will be determined and the ultrastructural characteristics of the synapses formed within this system will be described. The second objective will be to assess quanlitatively and quantitatively the effects of appropriately timed trigeminal lesions on the patterns of subsequent corticotrigeminal synaptogenesis within subnucleus interpolaris. Specifically tested will be the hypothesis that there is an age-dependent potential for synaptic reorganization within pars interpolaris following trigeminal rhizotomy, and that one of the factors responsible for this age-dependency for neuroplasticity is the extent of axoaxonic synapse formation at the time of the trigeminal rhizotomy.